Exercise in orbit
Claim in the list: To prevent muscle atrophy and fragile bones, crews in orbit exercise for several hours every day.
Verification: Largely supported for ISS crews, though “prevent” is too absolute. Microgravity reduces loading on muscles and bones, so crew members perform aerobic and resistance exercise on a treadmill, cycle, and resistive device. NASA reports an average of about two hours of exercise per day; schedules and protocols can vary. Exercise helps mitigate losses but does not guarantee complete prevention of musculoskeletal changes.
Conclusion: ISS astronauts typically exercise about two hours per day as a countermeasure to muscle and bone loss; this reduces risk but does not eliminate it completely.